1. Field of Invention
The invention relates generally to the field of wireless communication and data networks. More particularly, in one exemplary aspect, the invention is directed to methods and apparatus for multi-dimensional data permutation to increase transmission diversity in a wireless (e.g., cellular) network.
2. Description of Related Technology
Universal Mobile Telecommunications System (UMTS) is an exemplary implementation of a “third-generation” or “3G” cellular telephone technology. The UMTS standard is specified by a collaborative body referred to as the 3rd Generation Partnership Project (3GPP). The 3GPP has adopted UMTS as a 3G cellular radio system targeted for inter alia European markets, in response to requirements set forth by the International Telecommunications Union (ITU). The ITU standardizes and regulates international radio and telecommunications. Enhancements to UMTS will support future evolution to fourth generation (4G) technology.
A current topic of interest is the further development of UMTS towards a mobile radio communication system optimized for packet data transmission through improved system capacity and spectral efficiency. In the context of 3GPP, the activities in this regard are summarized under the general term “LTE” (for Long Term Evolution). The aim is, among others, to increase the maximum net transmission rate significantly in future, namely to speeds on the order of 300 Mbps in the downlink transmission direction and 75 Mbps in the uplink transmission direction. To improve transmission over the air interface to meet these increased transmission rates, new techniques have been specified.
MIMO (Multiple Input—Multiple Output) is one of the important techniques in LTE. MIMO is an antenna technology in which multiple antennas (up to four (4) antennas as an exemplary configuration) are used at both the NodeB (base station in LTE) and UE (mobile radio communication terminal) sides. An exemplary prior art MIMO implementation is illustrated at FIG. 1. Specifically, FIG. 1 illustrates a high-level MIMO transmission structure according to LTE that includes two independent data streams (Data Stream 1 102, Data Stream 2 104), and two antennas (Ant 1 106, Ant 2 108) at the transmitter side 110 and receiver side 112, respectively. In this example, the subcarriers may or may not be orthogonal between Ant 1 106, and Ant 2 108. At the transmitter side 110, the data symbols of each data stream are passed to the OFDM (Orthogonal Frequency Division Multiplex) modulator, where they are modulated onto the subcarriers. The block of output samples from the OFDM modulator make up a single OFDM symbol. This time-domain signal is then transmitted over the transmit antennas across the Mobile Radio Channel (MRC 1, MRC 2). At the receiver side 112 an OFDM demodulator is used to process the received signal and bring it into the frequency-domain (i.e., via Fast Fourier Transform (FFT) operation, or similar process). Ideally, the output of the OFDM demodulator will be the original symbols that were passed to the OFDM modulator at the transmitter.
In the field of telecommunications, significant research has been directed to correcting and or minimizing data corruption caused by imperfect communication channels. “Diversity schemes” are one such type of channel correction mechanism. A diversity scheme provides increased data robustness by utilizing two or more communication channels with different characteristics. Diversity schemes exploit the randomness of noise. In one illustrative scenario, the noise of each channel is uncorrelated to the noise of other channels; in contrast, the signal transmitted on each channel is correlated. Consequently, a combination of diversity streams increases the overall received signal power, without increasing the noise floor. Many diversity schemes currently exist and are used throughout the arts; such schemes include antenna diversity, coding diversity, constellation diversity, etc.
Unfortunately, existing diversity methodologies have at least one significant drawback. While the foregoing techniques may increase system performance to some degree, they do not maximally employ all the advantages offered by the full spectrum of possible diversity systems. Typical implementations only apply one diversity scheme at a time (e.g. HARQ coding diversity retransmits data which was previously “punctured” out). Generally, improved methods are needed for using the comparatively small number of diversity schemes to maximally improve signal robustness.
Accordingly, improved methods and apparatus are needed for increasing diversity in wireless communication systems, such as for example an LTE system. While individual mechanisms for providing a multitude of diversity (i.e., antenna, coding, constellation-bit mapping, etc.) modes in a wireless communication system have been contemplated, the prior art has failed to provide an intelligent approach for applying multiple diversity schemes in subsequent retransmissions. Accordingly, methods and apparatus for such intelligent combination of various diversity modes are desirable in order to improve on the retransmission performance of next generation wireless systems.
Such improved apparatus and methods would also ideally be applicable to maximize performance in both “open-loop” systems and “closed-loop” systems.